He had been informing the rally that the registration deadline had been extended as a result of Hurricane Matthew.
Mr Trump added his supporters should sign up for absentee ballots so their vote can be counted early.
The deadline extension in Florida had been opposed by the state's Republican governor Rick Scott and chairman of a Trump Super PAC.
While Mr Scott stated an 24-hour extension would be unnecessary - it took a lawsuit by the Florida Democratic Party and a Federal court decision to overrule his opposition.
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US District Judge Mark Walker stated in his decision an additional 100,000 people would be able to vote as a result of the extension, National Review reports.
A court hearing will convene on 12 October to decide whether a longer registration deadline should be introduced till 18 October.
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